Great article in the Seattle Times about the combination of (a) Canada's strict (stricter than in the United States) enforcement of DUI laws, coupled with the use of shared US-Canada criminal databases at border crossings. You get this at the end of a ferry ride from Washington state to Vancouver Island:
"During the May-to-September peak tourist season, four to five passengers a week are turned back by Canadian border agents at the Victoria dock. . . . 'We have witnessed firsthand people who haven't told their partner that at some point in their life they had a DUI. The first the wife learned about it was when the husband was denied entry.'"
So you can only imagine what will happen when high season at the upcoming Vancouver Olympics arrives.